Laser alarm system not working correctly..

[neba3939]

Hi guys, i am a first year college student and this is my first project to build by myself.. and i need help.
I build this laser alarm system and it works good. the Alarm sounds when the laser is broken and it stops when the laser is not interrupted. But the problem is when the laser is disturbed the alarm sounds but as soon as the laser touches the photocell again the alarm stops..
i was thinking, is there any way to make the alarm sound constantly non stop ones the laser is broken, Is it possible to make the alarm sound continuously without non stop unless it is stopped manually?
Please look at the schematics and help me..
thank you

 

[Harald Kapp]

Look up "RS flipflop", that's what you're going to need.
The SET input would be triggered by the Laser Alarm. The output will sound the alarm. The RESET input would be triggered manually to shut off the alarm.
Depending on the active level of the trigger signals (low active or high active) you may wire the Laser alarm and the manual trigger in the opposite order.


Harald